Method and apparatus for preventing corrosion in oil wells



Aug. 28, 1956 G. H. ROHRBACK METHOD AND APPARATUS FOR PREVENTING CORROSION IN OIL WELLS Filed July 22, 1952 FIG.3

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INVENTOR G/Lso/v H, ROHRBACK FIG.2

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ATTORNEYS United States Patent O METHOD AND APPARATUS FOR PREVENTING CORRSION IN OIL WELLS Gilson H. Rohrback, Whittier, Calif., assignor to California Research Corporation, San Francisco, Calif., a corporation of Delaware Application `luly 22, 1952, Serial No. 300,322

3 Claims. (Cl. 166-243) My invention relates to apparatus for injecting material at the bottom of a well, and particularly to apparatus for injecting corrosion inhibitors into an oil well.

Corrosion of ferrous metal surfaces in Contact with the producing streams of oil wells has long been recognized as a serious operating problem by petroleum producers. Considerable research effort has been directed to this problem, and several methods of reducing corrosion rates and therefore reducing the frequency of replacement of well tubing, sucker rods and other subsurface apparatus, have been proposed.

Chemists have found a number of solid compounds which satisfactorily retard corrosion. Examples of these products are sodium hydroxide. sodium carbonate `and sodium dichromate. However, the development of completely satisfactory methods of introducing these compounds into a well to effectively control corrosion has long been a problem upon which much time and elort has been spent to seek a `satisfactory solution.

According to prior art teachings of which l am aware, some of these solid corrosion inhibitor compounds are mixed with a weighting agent, such as metallic zinc, and are pelleted with a binding compound, such as alumina gel or starch. The pellets thus formed have a specific gravity appreciably greater than that of well fluids and are dropped into the well tubing at predetermined intervals of time to sink to the bottom of the hole and dissolve slowly, releasing corrosion prevention materials over a prolonged period of time. If properly applied, these pellets are capable of controlling corrosion over an extended period of time. However, production must be interrupted periodically for the application of these pellets and must not be resumed until they have fallen to a suflicient depth in the well `so that the corrosion inhibitor will contact the entire length of tubing and thus give optimum corrosion protection.

The corrosion problem is of suicient severity that such time-consuming corrosion inhibiting practices as described above are nevertheless followed in some wells. In other wells in which the corrosion problem is less aggravated, the expense of the use of pelleted corrosion inhibitors is too great economically to justify its use. In these cases, corrosion of the well equipment is accepted as the lesser of the two evils.

It is an object of my invention to provide an inexpensive method of using solid corrosion inhibitors effectively.

It is a further object of my invention to provide appa* ratus for injecting solid corrosion inhibitors into producing wells.

A further object of my invention is to provide a'device which can be placed adjacent the bottom of a producing oil well to release automatically over a prolonged period of time predetermined amounts or concentrations of a solid `corrosion inhibiting compound t-o eifectively provide protection from corrosion to the metal apparatus and equipment situated in the well.

l y lt is a further objectof my invention to provide apparatus for injecting solid chemical compounds at the bottom of oil Wells.

It is a still further object of -my invention to provide a metering system which will eject a Isolid chemical compound at a predetermined slow rate.

A number of solid corrosion inhibitors are commercially available which will adequately protect the metal parts of well equipment if applied at the rate of from l to parts per million of well water. If an adequate amount of such inhibitor could be placed at the bottom of a producing well and released at a rate slow enough to give only the desired concentration of inhibitor, a sufcient charge of inhibitor could be placed in the well at relatively infrequent intervals, of the order of one year, to provide protection from corrosion for this period.

To achieve maximum usefulness in the field, the injection device should be one which is compatible with the present types of well equipment. It is desirable that the injector have a maximum diameter no larger than the tub ing collars of the well. For convenience of use, it is desirable that it be' no longer than 50 feet, and preferably no longer than 30 feet. Desirably, it may have mechanical characteristics such that it need not be serviced during the time in which it is dispensing a charge of corrosion inhibitor. For convenience of use, it is desirable that it be self-contained in the sense that it not be connected to the pumping rrod or the electrical cables running through the annulus. An injector 40 feet long and having an inner chamber of 21/2 inches will have a capacity of approximately 4500 cubic inches. If the inhibitor is to be dispensed at the rate of 0.14 cc. per minute, it will remain available for a period of a year. Or stated differently, if the well-known inhibitor compound, sodium chromate (NazCrOfi'ZI-IzO), were dispensed continuously for a period of one year at the above rate, the inhibitor concentration continuously would be 25 p. p. m. in a well producing about 100 barrels of water daily. Wells can be treated successfully for corrosion control ywith injection of sodium dichromate at rates of about 25 p. p. m. active inhibitor.

For a solid injector to be acceptable to operating personnel of wells and to be practical from an economic viewpoint, it must be so arranged that it requires a minimum of attention over an extended period Iof time. By my invention I provide a metering system for use with solid corrosion inhibitors which is positive in operation, demands a minimum of attention, and is compatible with present well operating practices.

One embodiment of my invention comprises the use of pervious bags containing a corrosion inhibitor in solid form. The bags are contained within a perforated section of tubing and are lowered into the well. Well uids contact the inhibitor through the perforations in the tubing and through the bags. The inhibitor is dissolved at the rate required to maintain the desired concentration of inhibitor in the well uids.

The novel features which comprise my invention are set forth with more particularity in the accompanying claims. The invention itself, with respect to the details thereof, together with its additional objects and advantages, may be better understood from the following description of a specific embodiment with reference to the accompanying drawings, in which:

Figure 1 shows one embodiment of my invention using a single bag within a metal container.

Figure 2 shows a modification of my invention in which a plurality of exible bags are employed.

Figure 3 shows a bag containing inhibitor compounds.

Figure 4 shows a bag from which a portion of the inhibitor compound has been used.

Figure 5 shows a bag from which the inhibitor has been almost exhausted.

Figure 1 shows a specific embodiment of my invention which comprises the use of a metal container or basket 17 which is fastened to the lower end of the welil tubing 18 in a manner to lie adjacent to the bottom of the hole. Prior to fastening the container 17 to the tubing 18 there is placed in the container a porous bag containing a solid inhibitor compound. Above the portion 17 of the container is the lower part of the well tubing 19 which is perforated to permit uid to flow to the well pump. `It is to be understood that in a well which does not require a pump, the perforations permit well fluid to flow directly into the tubing.

The sides of the bag 20 are porous material such as woven glass liber or textile material. Well fluid ows through the slots of the container 17 through the mesh in the bag 21 to dissolve the inhibitor contained in the bag. The size of the mesh in the bag and the constituents of the inhibitor are so selected that the inhibitor is dissolved at the proper rate to provide the desired amount of inhibitor for the particular well uid. Examples of slow dissolving inhibitors are found in Patent No. 2,546,586, which issued to Walter M. Cross, Jr. One example set forth in this patent includes 55 parts plaster of Paris, 5 parts diatomaceous earth, 45 parts hydrated lime. As the inhibitor dissolves, it passes in solution form back through the bag walls and mixes with formation uid. It is then carried up the tubing string Where it protects exposed metal surface from corrosion. If the inhibitor itself is such that its dissolution rate tends to be too great, it is mixed or compounded with chemicals adapted to decrease its rate of dissolution. Alternatively, a different inhibitor having a different rate of dissolution is employed. The slotted portion 17 extends for substantially the entire length of the inhibitor-containing bag.

Figure 2 shows another arrangement of my invention. Below the perforated tubing 19, through which well fluid flows to the pump, is a metal container 21, preferably of 30 to 40 feet in length. Unlike the container just described, onlly the lower portion 23 of the container is slotted to admit well fluid. Within the section 21 can be contained one bag or a number containing corrosion inhibitors, only a predetermined number of which are exposed to well effluent at one time. Only the bag or bags near the bottom of the slotted container will be exposed to the action of the well uids. The length of the slotted portion can be selected to control the rate of inhibitor solution by controlling the amount of inhibitor exposed at one time.

Figure 3 shows a bag for holding inhibitor solids. The mesh 9 may be made of any flexible material which is pervious to well liquids and capable of withstanding Well fluids. Examples of such materials useful under certain Well conditions are nylon, wool, cotton or silk. Nylon is a generic term for any long-chained, synthetic polymeric amide which has recurred amide groups as an integral part of the main polymer chain, and which is capable of being formed into a filament whose structural elements are oriented in the direction of the axis. The top 11 and bottom 13 of the bag are rigid plates made preferably of an inert material such as Bakelite Bakelite is a trade name that covers a large group of thermo-setting phenolic and urea resins. The bag is so constructed that it may be filled from the top before the bakelite top plate 11 is atlixed to the bag. Between the top 11 and bottom 13 is a resilient band 1S such as a cylinder of rubber or a coil spring. The band 15 exerts a substantially uniform radial force tending to collapse the mesh 9 toward the center of the bag, for a purpose to be explained hereinafter. The bag may have a height between the top 11 and bottom 13 of a few inches to several feet. A longer bag wilt require several bands 15 to facilitate ordered collapsing. According to a preferred embodiment of my invention, however, the height of the bags is approximately 2 feet, and a number of these bags are placed to till the container 21. Well uid 4 ows through the slots in the portion 23 and the mesh 9 of the bags 25, dissolving the inhibitor from the lowermost bags which are in the slotted portion 23.

In a preferred embodiment of my invention, the well tluid is in contact only with the lowermost bags. The diameter of the bags 25 is substantially the same as the inner diameter of the tube 21. The bags are introduced into the container, and the container is then attached to the tubing string to be run into the hole. Since the top of the metal containeris sealed, well gas will soon become entrapped and will thereafter prevent contact of the inhibitor bags by well fluid until the lower exposed bags are emptied. Accordingly, well uid is restrained by the gas pressure from owing up the inside of the container to wet all ofthe bags of inhibitor.

As the inhibitor in the lower bags is dissolved, the bags begin to collapse under pressure from the bags above them in the manner shown in Figure 4. The band 15 compresses the mesh, causing it to collapse inwardlyyaud the top 11 and bottom 13 approach each other until the bag is fully collapsed into the form shown in Figure 5. The rst bags then are compressed into a small space at the bottom of the container 23, and other bags fall down to take their place in the slotted portion 23 of the container. There is, then, a constant dissolution of the inhibitor compounds and a constant replacement of the exhausted inhibitor bags. The length of the slotted portion 23 is selected to restrict the contact of well uid over the inhibitor sufficiently to retard the rate of dissolution of the inhibitor until the proper ratio of inhibitor to well fluid is maintained.

It is to be noted that the exhausted bags 2S will occupy a portion of the slotted portion 23 of the container, thereby restricting the contact of well duid over inhibitorcontaining bags. This is a valuable attribute of my invention, as will be shown by the following example. I have found that bags can be employed which will collapse to less than one-twentieth their height when suiciently charged. Thus, for a bottom hole injector container feet long with a slotted end piece of 5 feet, only about 11/2 feet of the slotted piece will be occupied by collapsed bags when the last charge is dissolving. This will mean that the initial solution rate will exceed the final solution rate by 40 per cent. It is desirable, however, to have such a more rapid initial solution rate to build up the inhibitor iilm on the metal surface. Thereafter, the rate of dissolution of the inhibitor may properly be decreased without unduly decreasing the corrosion inhibiting powers. By the proper selection of inhibitor, the abovedescribed apparatus will restrain corrosion for a year or more without attention by the well operating crew. At the end of this time, the inhibitor bags may be removed and a new set of bags lowered into the well. The bags can be replaced when the tubing string is drawn. The tubing string is then replaced in the well with a new charge of inhibitor.

The use of solid inhibitor in pellet form would be highly satisfactory. If pellets were used, the bags could be omitted in the dispensing apparatus shown in Figures 1 and 2.

Although I have shown and described preferred embodiments of my invention, it will be apparent that many modifications thereof are possible without departure from the spirit and scope of the invention, as defined in the appended claims. For example, my invention may be used to introduce materials other than corrosion inhibitor into an oil well.

I claim:

1. For use in injecting corrosion inhibitor into the iluids of a well, the combination comprising a section of tubing at the bottom of said well, perforations in a lower section of said tubing, a plurality of flexible uid pervious bags containing said inhibitor, said bags each having a diameter substantially equal to the inside diameter of said tubing, the combined height of said bags in said tubing being greater than the height of the perforations in said tubing, said bags being adapted to be placed Within said section of tubing and to feed down said tubing as the inhibitor is dissolved.

2. A device for dispensing predetermined concentrations of a corrosion inhibitor into well uids adjacent the bottom of a well comprising in combination a perforated rigid container placed adjacent the bottom of the well, a corrosion inhibitor in solid form and adapted to be dissolved by said well uids placed in said container, the perforations of said rigid container being at levels lower than the top of said corrosion inhibitor.

3. A device for maintaining a predetermined concentration of corrosion inhibitor in fluids in a well comprising a perforated container placed adjacent the bottom 15 2437475 inhibitor in solid form, and adapted to be dissolved by said fluids, placed in said container and exposed to said uids through the perforations of the container, the perforations of the container extending to a height lower than the top of the corrosion inhibitor, said corrosion inhibitor being adapted to move downward in said container as lower portions of said corrosion inhibitor are dissolved in the tluids.

of the well, a corrosion References Cited in the le of this patent UNITED STATES PATENTS Re. 23,583 Eilerts Nov. 18, 1952 1,873,084 Walker Aug. 23, 1932 Oxford Mar. 9, 1948 

1. FOR USE IN INJECTING CORROSION INHIBITOR INTO THE FLUIDS OF A WELL, THE COMBINATION COMPRISING A SECTION OF TUBING AT THE BOTTOM OF SAID WELL, PERFORATIONS IN A LOWER SECTION OF SAID TUBING, A PLURALITY OF FLEXIBLE FLUID PERVIOUS BAGS CONTAINING SAID INHIBITOR, SAID BAGS EACH HAVING A DIAMETER SUBSTANTIALLY EQUAL TO THE INSIDE DIAMETER OF SAID TUBING, THE COMBINED HEIGHT OF SAID BAGS IN SAID TUBING BEING GREATER THAT THE HEIGHT OF THE PERFORATIONS IN SAID TUBINGS, SAID BAGS BEING ADAPTED TO BE PLACED WITHIN SAID SECTION OF TUBING AND TO FEED DOWN SAID TUBING AS THE INHIBITOR IS DISSOLVED. 